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Description:
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The goals of this work were to synthesize high performance perovskite based thin film
solid oxide fuel cell (TF -SOFC ) cathodes by pulsed laser deposition (PLD ) , to study the
structural , electrical and electrochemical properties of these cathodes and to establish
structure -property relations for these cathodes in order to further improve their properties
and design new structures .
Nanostructured cathode thin films with vertically -aligned nanopores (VANP ) were
processed using PLD . These VANP structures enhance the oxygen -gas phase diffusivity ,
thus improve the overall TF -SOFC performance . La0 .5Sr0 .5CoO3 (LSCO ) and
La0 .4Sr0 .6Co0 .8Fe0 .2O3 (LSCFO ) were deposited on various substrates (YSZ , Si and
pressed Ce0 .9Gd0 .1O1 .95 (CGO ) disks ) . Microstructures and properties of the
nanostructured cathodes were characterized by transmission electron microscope (TEM ) ,
high resolution TEM (HRTEM ) , scanning electron microscope (SEM ) and
electrochemical impedance spectroscopy (EIS ) measurements . A thin layer of vertically -aligned nanocomposite (VAN ) structure was deposited in
between the CGO electrolyte and the thin film LSCO cathode layer for TF -SOFCs . The
VAN structure consists of the electrolyte and the cathode materials in the composition of
(CGO ) 0 .5 (LSCO ) 0 .5 . The self -assembled VAN nanostructures contain highly ordered
alternating vertical columns formed through a one -step thin film deposition using a PLD
technique . These VAN structures significantly increase the interface area between the
electrolyte and the cathode as well as the area of active triple phase boundary (TPB ) ,
thus improving the overall TF -SOFC performance at low temperatures , as low as 400oC ,
demonstrated by EIS measurements . In addition , the binary VAN interlayer could act as
the transition layer that improves the adhesion and relieves the thermal stress and lattice
strain between the cathode and the electrolyte .
The microstructural properties and growth mechanisms of CGO thin film prepared by
PLD technique were investigated . Thin film CGO electrolytes with different grain sizes
and crystal structures were prepared on single crystal YSZ substrates under different
deposition conditions . The effect of the deposition conditions such as substrate
temperature and laser ablation energy on the microstructural properties of these films are
examined using XRD , TEM , SEM , and optical microscope . CGO thin film deposited
above 500 ºC starts to show epitaxial growth on YSZ substrates . The present study
suggests that substrate temperature significantly influences the microstructure of the
films especially film grain size . |